US3739863A

US3739863A - Reciprocating linear hydraulic motors

Info

Publication number: US3739863A
Application number: US00149217A
Authority: US
Inventors: M Wohlwend
Original assignee: Individual
Current assignee: Stanley Works
Priority date: 1971-06-02
Filing date: 1971-06-02
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19
Also published as: CA957589A

Abstract

Supplied hydraulic fluid pressure overcomes the force of a spring and moves a valve member, which is biased towards a closed position by the spring, into an open position, opening a passageway to admit the hydraulic fluid to a radial pressure surface on a linear piston. The hydraulic fluid pressure acting on the piston moves the piston against the spring, compressing the spring. When the piston reaches its retracted position hydraulic fluid pressure is added to the spring pressure causing the valve member to move downwardly into a position in which the fluid pressure is released from the pressure surface on the piston, enabling stored energy in the spring to forcibly drive the piston through a power stroke.

Description

il'iiite Patent [191 Wohlwend RECIPROCATING LINEAR HYDRAULIC MOTORS [76] Inventor: Maurice Wohlwend, 5001 South 112th Street, Seattle, Wash. 98178 [22] Filed: June 2, 1971 [21] Appl. No.: 149,217

92/134,173/134 [51] Int. Cl B25d 9/00 [58] Field of Search 173/119, 120, 134,

45 June 19, 19

8/1969 James 173/119 2/1972 Coyne 173/119 [5 7] ABSTRACT Supplied hydraulic fluid pressure overcomes the force of a spring and moves a valve member, which is biased towards a closed position by the spring, into an open position, opening a passageway to admit the hydraulic fluid to a radial pressure surface on a linear piston. The hydraulic fluid pressure acting on the piston moves the piston against the spring, compressing the spring. When the piston reaches its retracted position hydraulic fluid pressure is added to the spring pressure causing the valve member to move downwardly into a position in which the fluid pressure is released from the pressure surface on the piston, enabling stored energy in the spring to forcibly drive the piston through a power stroke.

33 Claims, 19 Drawing Figures Sim 1 N 5 PAINTED- ,MJKMMJ PAIENIED m w BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to reciprocating linear hydraulic motors, and more particularly to such motors of a type including a linear piston or hammer which is driven through its power stroke by energy stored in a gaseous or mechanical spring, and in which hydraulic fluid pressure is employed for retracting the piston and storing energy in the spring.

2. Description of the Prior Art The body of technology relating to reciprocating hydraulic linear motors is quite large and includes many different ways of moving a piston or working member through a power stroke. It is known to use hydraulic fluid pressure for both driving and retracting the piston or working member. Examples of this type of motor are shown by U. S. Pat. No. 3,4l1,592 granted on Nov. 19, 1968 to Roger Montabert, and by U. S. Pat. No. 3,339,644 granted Sept. 5, I967 to Ernest F. Klessig. It is also known to move the piston in one direction by the application of hydraulic fluid pressure pulses to the piston, and then move itin the opposite direction by use of a spring. U. S. Pat. No. 3,456,741 granted July 22, 1969 to David Richard James discloses a motor of this type in which the piston is driven through a forward power stroke by the springand is returned or retracted by fluid imposed pressure pulses, to store energy in the spring, The present invention relatesto the provision of improved motors of this. general type, characterized by a simplicity of overall design a minimum of parts, relatively low manufacturing costs, ease of assembly, disassembly, and maintenance, and reliability throughout a long life of repetitious use.

SUMMARY OF THE INVENTION Motors of the present invention characteristically comprise a fluid or mechanical spring for driving a piston type power element or hammer through its power stroke, and a simple system for delivering hydraulic fluid pressure 'againstrthe piston for the purpose of retracting it and storing energy in the spring and at this time exhausting fluid-from the motor housing. In preferred form, the motors of this invention include a sin? gle reciprocating linear valve member for controlling the delivery of fluid pressure to the piston. All valving functions are performed by this member and the piston in conjunction with flow passageway in the motor housing, the piston and the valve member. The valvemem-. her is biased towards a by-pass position by the fluid or mechanical spring. Inflowing hydraulic fluid is first directed against a transverse or radial surface on the valve member, to exert a force on the valve member of sufiicient magnitude to overcome the spring force and move the valve member into a supply position. This communicates the inflowing hydraulic fluid with a transverse or radial pressure surface on the piston, resulting in the hydraulic fluid exerting a force on the pis-v ton in opposition to the spring force, causing retraction of the piston. While retracting the piston forces the used hydraulic fluid to be exhausted from the motor housing and also stores energy. in the spring. when the piston reaches its fully retracted position passageways are opened through which hydraulic fluid pressure is delivered to a transverse or radial pressure surface on the valve member facing the spring, so that the hydraulic fluid pressure is added to the spring force. Together the spring and hydraulic fluid exert a force on the valve member of sufficient magnitude to return the valve member to its by-pass position. When the valve member is in its by-pass position inflow of additional hydraulic fluid is prevented and the fluid pressure is removed from the pressure surface on the piston, freeing the spring to drive the piston through its power stroke. During the power stroke this fluid is moved by the piston into an upper expansible chamber bounded in part by a surface on the piston (i.e. the moving boundary of the chamber) which is directed oppositely from said pressure surface. Then, during piston retraction the piston moves such fluid] out of this chamber and the motor casing back to the supply pump.

An important feature of the invention relates to the provision of means for isolating the piston from the spring force after the piston delivers a blow to an impact member or the like but before such hammer strikes any portion of the casing in which it is housed, so that the piston is not driven hard against a portion of the casing but rather is allowed to coast to a stop before reversing its direction of travel.

Another important feature involves the provision of a body of cushioning fluid to function as a stop for the piston at the end of its power stroke, so that it never impacts directly against the housing. 7

Other features of the invention will be apparent from the following description and accompanying sheets of drawing. A

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a hand type impact tool incorporating a reciprocating linear hydraulic motor embodying the invention;

FIG. 2 is an enlarged scale, fragmentary, axial sectional view of the motor, with some parts shown in side elevation, such view showing the piston at rest and the valve member in its by-pass position;

FIG. 3 is a view like FIG. 2, but showing the control valve raised by incoming hydraulic fluid into its supply position;

FIG. 4 is a view like FIGS. 2 and 3, but showing the piston partially raised by the hydraulic fluid;

FIG. 5 is a view like FIGS. 2-4, but showing the piston raisedan additional amount by the hydraulic fluid;

FIG. 6 is a view like FIGS. 2-5,. but showing the piston fully raised into its retracted position and the control valve member returned to its bypass position;

FIG. 7 is a cross-sectional view taken through FIG. 2, substantially along line 7--7 thereof;

FIG. 8 is a fragmentary axial sectional view taken substantially along line 8-8 of FIG. 7;

FIG. 9 is a cross-sectional view taken substantially along line 9--9 of FIG. 2;

FIG. 10 is another cross-sectional view taken substantially along line 10--l0 of FIG. 2;

FIG. 11 is another cross-sectional view taken substantially along line 11-11 of FIG. 2;

FIG. 12 is an axial sectional view of a modified form of motor characterized by a side placed valve element;

FIG. 13 is a cross-sectional view taken substantially along line 13-l3 of FIG. 12;

FIG. 14 is a cross-sectional view taken substantially along line 14l4 of FIG. 12;

FIG. 15 is a cross-sectional view taken substantially along line l5-15 of FIG. 12;

FIG. 16 is a cross-sectional view taken substantially along line 16-16 of FIG. 12;

FIG. 17 is a cross-sectional view taken substantially along line 17-17 of FIG. 12;

FIG. 18 is a cross-sectional view taken substantially along line 1818 of FIG. 12; and

FIG. 19 is a cross-sectional view taken substantially along line l919 of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a preferred type of utilization device for the motor of this invention. It is a hand held breaker tool T adapted to be an accessory for an item of power equipment, such as an earth working machine or the like, of a type which includes a hydraulic power system. When needed, the breaker tool is merely connected into the hydraulic system of such machine to be powered thereby, making it unnecessary for the workman to bring a more conventional pneumatic breaker tool to the work site. Of course, it is to be understood that the motor of this invention has general utility and can be used wherever a linear motor requiring its capabilities is needed.

Referring now to FIGS. 2-11, in preferred form the motor of this invention is shown to comprise an elongated sectional casing or housing-l formed to include an elongated inner cavity 12. A hammer or piston 14 is supported for axial reciprocating movement within the cavity 12. The upper portion 16 of cavity 12 is charged with a gas (e.g. nitrogen) under substantial pressure. This gas functions as a spring for (1) driving the piston 14 downwardly through its power stroke and (2) biasing a valve member towards a by-pass position, as will hereinafter be explained in detail. I

Piston 14 has an intermediate portion 18 of a first diameter which is machined to include a girth groove or annular channel 20. Piston 14 also includes a smaller diameter striker portion 22 at its lower end and a reduced diameter upper end portion 24 which receives the force of the gas spring. Striker portion 22 is snugly accommodated within a bore 26 formed through a lower portion 28 of housing 10. A suitable seal 30 (e.g. a chevron seal) is provided to seal against leakage between the surfaces of the striker portion 22 and the bore wall 26.

The upper end portion 24 of piston 14 is relatively snugly received within a cup-like member 32. This member 32 comprises a transverse end wall 34 and a tubular side wall 36 extending axially from end wall 34 in surrounding relationship to the upper end portion 24 of piston 14. The compressed gas spring does not act directly on the piston part 24, but rather exerts itself on the transverse wall 34 and throughout most of the operating cycle wall 34 in turn transfers the force to the piston part 24.

The casing includes an internal annular wall 38 in which the upper portion of an axially reciprocating sleeve valve member 40 is received. The tubular side wall 36 of cup member 32 is slidably received in an upper bearing portion 42 of valve member 40. The bearing 42 is both internally and exteriorly grooved to receive sealing rings 46. In preferred form the bearing 42 is separate from the rest of valve member 40 but the two pieces move together and function as one.

The lower end portion of sleeve valve member 40 snugly surroundingly engages the intermediate portion 18 of piston 14. The lower end portion of member is snugly received within a casing part 48 and is externally grooved to receive a sealing ring 50 for sealing against fluid leakage between the surfaces of the

parts

40, 48.

Inlet passageways 52 for inflowing hydraulic fluid are formed longitudinally through a side wall portion of the housing 10 from an off-on control valve 54 (FIG. 1) at the upper end of the housing 10 down to an annular chamber 56 formed in the lower portion 28 of casing 10 generally below the lower end surface 58 of sleeve valve member 40. An annular chamber 60 is defined radially between the annular lower end portion 62 of sleeve valve member 40 and the striker portion 22 of piston 14, and axially between a radial surface 41 on the lower end portion 28 of housing 10 and an opposing radial surface 43 on the intermediate portion 18 of piston 14. Herein this surface 43 will be referred to as the pressure surface. The boundary to chamber 60 provided by housing portion 28 is a transverse end wall 41 against which the transverse lower end surface 58 of valve member 40 is seated when the valve member 40 is in the position shown by FIG. 2 of the drawing (i.e. in its by-pass position).

A plurality of axial passageways 66 are formed in the intermediate portion 18 of piston 14 for communicating chamber 60 with girth groove 20.

When the piston 14 and the valve member 40 are in l the positions shown by FIG. 2 hydraulic fluid flowing into chamber 56 first contacts end surface 58 of valve member 40. At this time the opposite end surface of valve member 40 is subjected to the downwardly biasing force of the gas spring, as is the piston 14 through cup wall 34. The inflowing hydraulic fluid in chamber 56 exerts a force on the lower end surface 58 sufficient to overcome the gas spring force exerted on upper end surface 70. As a result, the inflowing hydraulic fluid forces sleeve valve member 40 upwardly until the annular shoulder 72 thereon contacts the annular stop 74. The inflowing hydraulic fluid now flows from chamber 56 through chamber 60, then through axial passageways 66 into the girth groove 20. It also exerts an axially upwardly directed force against the pressure surface 43. This subjects the piston 14 to an upward force of a magnitude sufficient to overcome the downwardly biasing force of the pressure spring acting on piston 14 through wall 34. This causes the piston 14 to be moved upwardly from the position shown by FIG. 3, through the intermediate position shown by FIG. 4, and into the position shown by FIG. 5.

In FIG.4 the annular chamber 20 is approaching registry with a plurality of radial ports 76 extending through a side wall portion of sleeve valve member 40. Ports 76 communicate the inside of member 40 with an annular expansion chamber 78 formed by and axially between opposing radial surfaces on the inner wall 38 and on a piston ring 79 carried by the sleeve valve 40. When the ports 76 come into registry with chamber 20 (FIG. 5) some of the hydraulic fluid flows through the ports 76 and exerts a downwardly acting force on the annular piston surface 80. The sum of the fluid spring force acting on surface and the hydraulic fluid force acting on piston surface 80 is larger than the force exerted by hydraulic fluid on valve member surfaces 58 and 72, resulting in the valve member 40 being moved downwardly into its by-pass position. This moves the annular shoulder 72 of valve member 40 out from contact with the stop surface 74 and opens an annular passageway 82. The seated lower end portion 62 of valve member 40 stops (i.e. blocks) inflow of additional hydraulic fluid into the chamber 60. The fluid already in chamber 60 is exhausted therefrom through the radial ports 84 into the annular space 86 and from the annular space 86 through the newly created passageway 82 into the annular by-pass chamber 88. A plurality of axial ports 90 communicate chamber 88 with a collector chamber 92 and return passageways 94 extend from chamber 92 up to conduit means extending back to the pump (not shown).

When chamber 60 comes into communication with by-pass chamber 88 the pressure exerted by the by draulic fluid on pressure surface 43 is released, allowing the stored energy of the gas spring to be released for driving the piston 14 downwardly through its power stroke. The expansible chamber 104 above intermediate portion 18 of piston 14 changes volume at substantially the same rate as chamber 60. During the power stroke the fluid removed from pressure surface 43 is merely transferred from chamber 60 through

passageways

82, 108, 106 into chamber 104.

The gas does not act directly on the piston 14, but rather acts on wall 34 which transmits the driving force to the piston 14 until the peripheral lip 96 of member 34 contacts the annular stop member 98. Member 98 is preferably a bellville type spring so that it will cushion the stop of end wall 34. Wall 34 seats against spring 98 after the striker portion 22 of piston 14 has struck the anvil of the breaker tool 100 but while piston surface 102 is still spaced from wall 64. When wall 34 is seated on the spring 98 the force of the fluid spring is removed from the upper end portion of the piston 14 and the piston 14 is free to coast to a stop. Also, as best shown in FIG. 2, a cushion of hydraulic fluid always remains in the chamber 60 and provides a fluid stop for the piston during the driving stroke.

The gas spring serves to cushion the piston 14 at the end of its upward travel at the end of the return stroke. Annular lip 105 prevents cup member 32 from traveling up into gas chamber 16 in the event it gets away from piston 14.

When the piston 14 moves downwardly it communicates chamber 78 with the chamber 88 via radial ports 76, annular chamber 104, and

radial ports

106 and 108. The chamber 78 remains exhausted until the piston 14 is again moved upwardly a distance sufficient to place the seal ring 19 above the radial ports 76 (FIG. 5). Seal ring 19 is preferably a split metal sealing ring like the type used on the pistons of internal combustion engines. This is so it willnot be distorted by fluid pressure when it passes across ports 76. During retraction of the piston 14 there is a positive displacement of the fluid from chamber 104 out through ports 106, s, chamber 88, ports 90, chamber 92, and passageways 94, back to the supply pump (n ot shown).

One or more surge chambers may be provided in the chamber 88. In the preferred embodiment these chambers are shown to be inwardly bounded by a flexible wall 112 and outwardly bounded by a solid wall 114 shown to clamp an annular portion of the flexible wall 1 12 between it and a portion of the casing 10, immediately bounding the chamber 1 10. Air or some other gas is trapped inside each chamber 110. When a pressure surge occurs within the chamber 88 it merely forces the flexible walls 112 into the chambers 110 and in this manner is dampened.

In operation, hydraulic fluid supplied to annular chamber 56 exerts itself on the lower end surface 58 of valve member 40 and exerts an upwardly directed endwise force on the valve member 40 of sufficient magnitude to overcome the downwardly directed force of the gas spring acting on surface 70. The valve member 40 is moved upwardly by the hydraulic fluid pressure until the annular shoulder 72 contacts and is stopped by the annular stop 74 (FIG.v 3). The hydraulic fluid then moves from space 56 under valve member portion 62, into chamber 60, and from chamber 60 through the passageways 66 into annular groove 20. In chamber 20 the fluid exerts an upwardly directed force on surface 43, causing the piston 14 to move upwardly relative to reaction surface 41 on housing 18 below the piston surface 43, and in opposition to the gas spring force exerted on wall 34 and by it against the upper end of piston 14.

Once sealing ring 19 passes above the radial ports 76 (FIG. 5) the fluid in chamber 20 flows therefrom radially out-wardly through the ports 76 and into the expansible chamber 78 above the annular piston ring 79. The hydraulic fluid force on piston surface 80, and the gas spring force on surface 70, act together to force the valve member 40 endwise downwardly until the lower surface 58 is again seated on housing surface 41 (FIG. 6). Such movement of valve member 40 opens annular passageway 82, communicating chamber 60 with the by-pass chamber 88. In that manner the upwardly directed force is removed from the piston 14. Then, the stored energy in the gas piston exerts itself on wall 34 and through wall 34 onto the upper portion 24 of the piston 14, and forces the piston 14 downwardly through a power stroke. As shown by FIG. 6, when valve member 40 is seated and the piston 14 is retracted fluid is trapped in chamber 78. As a result valve member 40 is held in its seated position until the piston 14 has been driven downwardly.

In the illustrated embodiment the piston 14 is forced downwardly by the compressed gas until the lower end of its striker portion 22 hits the upper end (not shown) of a moil point (FIG. 1). This contact occurs while piston surface 43 is still spaced a sufficient distance above housing surface 41. The force of the compressed gas is applied on the piston 14 until the flange 96 on cup member 32 makes contact with and is stopped by the annular spring 98. This seating of flange 96 on spring 98 also occurs at a point of time when piston surface 43 is spaced upwardly from housing surface 41. As a result, the piston 14 is not forcibly driven by the compressed gas against a portion of the housing. Rather, once cup member 32 seats itself on spring stop 98, the piston 14 coasts to a stop before changing its direction of travel. As best shown by FIG. 2, the piston surface 43 never does contact housing surface 41 because an annular body of the incompressible hydraulic fluid becomes trapped axially between piston surface 43 and housing surface 41 when the piston 14 is in the position shown by FIG. 2. This annular body of hydraulic fluid functions as a fluid stop for the piston 14.

The piston 14 is cushioned in the upper direction by the compressed gas spring and in the downward direction by the hydraulic fluid in chamber 60.

Reference is now made to the secondary embodiment of the invention shown by FIGS. 12-19. This embodiment diflers from the embodiment of FIGS. 2-11 in that its reciprocating valve member 116 is spaced laterally from the piston 118. However, the operation of this form is almost the same, as will presently be seen.

In the embodiment shown by FIGS. 12-19 the incoming hydraulic fluid travels from suitable valving (not shown) atop the housing 120 down through a longitudinal inlet passageway 122, into an annular chamber 124, and thence through radial ports 126 into chamber 128 located below the valve member 116. It then presses upwardly against the lower end surface 130 of valve member 116, forcing valve member 116 upwardly off from its seat 118. This communicates chamber 128 with an annular passageway 134 which is connected by ports 136 and a passageway 138 with an annular chamber 140 defined axially between a lower radial surface 142 on piston 118 and an opposing radial surface 144 on housing 120.

The hydraulic fluid flows from annular chamber 140 through axial passageways 143 into annular girth chamber 146 formed in the piston 1 18 closely below a metal sealing ring 148 which surrounds a midportion of the piston 118. The hydraulic fluid exerts an upwardly directed force on piston surface 142, in opposition to a downward force provided by a fluid spring within chamber 152. The hydraulic fluid lifts piston 118 upwardly relative to reaction surface 144 until sealing ring 148 is above the radial ports 154. At this point of time the shoulder 155 on valve member 116 is against stop member 156. The hydraulic fluid flows from chamber 146 through the ports 154 into the expansible chamber 158 above radial surface 160 on valve member 116. The hydraulic fluid exerts a force on surface 160 which is added to the force exerted by the gas in chamber 152 on upper end surface 162, and together I they move the valve member 116 downwardly until the surface 130 is again seated on the surface 118. When this happens chamber 140 is communicated through annular passageway 163 to a housing chamber 166 and from there into the hollow body of valve member 116 through radial ports 168. The fluid emerges from an upper set of radial ports 170 into an upper passageway 172 and thence into chamber 173. Once the fluid pressure is relieved from piston surface 142 the gas spring acts to forcibly drive the piston 118 downwardly through its power stroke. The piston 118 moves downwardly until its striker portion 176 strikes a blow against the moil point 178. Shortly after this happens the annular flange 180 at the periphery of end wall 82 on drive member 184 contacts and is stopped by annular spring 186. As in the earlier embodiment, this isolates the compressed gas spring from the piston 118 which then coasts to a stop against an annular body of hydraulic fluid trapped within the chamber 140.

In this embodiment the valve member 116 is provided with a sealing ring 188 positioned to ride housing wall 190, and a smaller ring 192 arranged to ride housing wall 194. The other sealing rings illustrated may be chevron type packings, for example.

As in the earlier form, when valve member 116 is seated and piston 118 is retracted flow through ports out from chamber 158, through ports 154, and into chamber 172. I

The invention maybe embodied in other specific forms without departing from the spirit or central characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the fore- 154 is blocked and fluid is trapped within chamber 158 going description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed is: 1. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by atransverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; 7 hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a linear reciprocating valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for mov ing the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, said valve member having a first end portion which is in communication with the inflowing hydraulic fluid and receives an endwise force therefrom tending to move said valve member towards its first position, a second end portion, biasing force means acting on said second end portion and tending to move the valve member towards its second position, with said inflowing hydraulic fluid by itself exerting a force on said valve member that is larger than then biasing force, said valve means further comprising means for directing some of the hydraulic fluid against the valve member, to exert a force on the valve member acting in the same direction as the biasing force when the valve member is in its first position, with the combined forces of said biasing force means and said hydraulic fluid being larger than the force of said inflowing hydraulic fluid and being sufficient to move said valve member into its second position. i 2. A motor according to claim 32, wherein the spring means is a body of a compressible fluid sealed within a chamber which is expansible towards the piston.

3. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity;

spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall;

hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, wherein said valve member is annular and surrounds a portion of said piston, said valve member includes a first end surface which is seated against a portion of said transverse surface when the valve member is in its second position, and a second end surface which is subjected to the force of the spring means, such force tending to urge the valve member towards said transverse surface, and said housing includes passageway means for delivering hydraulic fluid to the first end surface of said valve member, for exerting a force on said first end surface which moves the valve member from its second position into its first position. i

4. A motor according to claim 3, wherein said housing includes an internal tubular guide for said valve member in which said valve member moves, means forming a bypass chamber which at least partially surrounds the valve member, said valve member including side wall opening means through which the hydraulic fluid flows from the piston pressure surface into said by-pass chamber when the valve member is in its sec ond position and the piston is traveling through its power stroke.

5. A motor according to claim 4, wherein said housing includes means forming an internal annular seat generally at the entrance to said exhaust chamber, and said valve member includes an exterior annular closure portion which seats tightly against said seat when the valve member is in its first position, and prevents hydraulic fluid from flowing into the by-pass chamber so that it instead exerts a force on the pressure surface of the piston.

6. A motor according to claim 5, wherein the tubular guide for said valve member includes means forming an expansible chamber with said valve member, in surrounding relationship to said valve member, and said valve member includes apiston ring portion defining a movable wall of said chamber, and said valve member includes side wall opening means through which the hydraulic fluid flows from the region of the piston pressure surface into said expansible chamber when the valve member is in its first position and the piston is'retracted against the spring means, whereby the hydraulic fluid exerts a force on said piston ring which in combination with the spring means force on the valve member acts to move the valve member from its first position into its second position.

7. A motor according to claim 6, wherein said motor includes passageway means for exhausting the fluid from the expansible chamber into the by-pass chamber when the valve member is in its second position and the piston is moving through its power stroke.

8. A motor according to claim 7, wherein said housing includes a separate cavity for said valve member which is offset from the piston cavity, and said valve member includes a first end surface which is seated against a portion of said transverse surface when the valve member is subjected to the force of the spring means, such force tending to urge the valve member towards said transverse surface, and said housing includes passageway means for delivering hydraulic fluid to the first end surface of said valve member, for exerting a force on said first end surface which moves the valve member from its second position into its first position.

9. A motor according to claim 8, wherein said housing includes means forming a by-pass chamber which at least partially surrounds the valve member, said valve member including side wall opening means through which the hydraulic fluid from the piston pressure surface is exhausted when the valve member is in its second position and the piston is moving through its power stroke.

10. A motor according to claim 9, wherein said housing includes means forming an internal annular scat generally at the entrance to said by-pass chamber, and said valve member includes an exterior annular closure portion which seats tightly against said seat when the valve member is in its first position, and prevents hy' draulic fluid from flowing into the by-pass chamber so that it instead exerts a force on the pressure surface of the piston.

11. A motor according to claim 10, wherein the cavity for said valve member includes means forming an expansible chamber with said valve member, in surrounding relationship to said valve member, and said valve member includes a piston ring portion defining a movable wall of said chamber, and said housing includes passageway means through which the hydraulic fluid flows from the region of the piston pressure surface into said expansible chamber when the valve member is in its first position and the piston is retracted against the spring means, whereby the hydraulic fluid exerts a force on said piston ring which in combination with the spring means force on the valve member acts to move the valve member from its first position into its second position.

12. A motor according to claim 11, wherein said motor includes passageway means for exhausting the fluid from the expansible chamber when the valve member is in its second position and the piston has moved substantially through its power stroke.

13. A linear reciprocating motor comprising:

a housing including an elongated piston cavity defined in part by a transverse wall;

an elongated piston in said cavity;

hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall, and means for delivering a hydraulic fluid to said surface, including control valve means movable between a first position inwhich the hydraulic fluid is admitted to the pressure surface, for moving the piston against the spring means and compressing the latter, and a second position in which the hydraulic fluid is exhausted from the pressure surface, resulting in the piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall; and

limit means for isolating the piston from the force of said spring means before the piston reaches the transverse wall, so that the piston is not driven hard against the transverse wall by the spring means but is free to coast to a stop position as it approaches the transverse wall before reversing its direction of travel.

14. A motor according to claim 13, wherein a fluid containing chamber exists axially between saidv transverse wall and said piston and the fluid therein provides a cushioning stop for said piston.

15. A motor according to claim 13, wherein the spring means is a body of a compressible fluid sealed within a chamber which is expansible towards the piston.

16. A motor according to claim 15, wherein the limit means comprises a barrier for the fluid spring chamber and means for arresting movement of said barrier independently of said piston, positioned so that the barrier is stopped before the piston reaches said transverse wall and serves to isolate the spring force from the piston. i;

17. A motor according to claim 16, wherein a fluid containing chamber exists axially between said transverse wall and said piston and the fluid therein provides a cushioning stop for said piston.

18. A motor according to claim 16, wherein an axial wall means is connected to said barrier and is in part at least tubular and outwardly bounds at least a portion of said piston.

19. A motor according to claim 18, wherein a bearing is radially received between said axial wall means and an inner side wall portion of the cavity for guiding said axial wall means.

- 20. A motor according to claim 15, wherein the stop member for said wall means is a mechanical spring.

7 21. A motor according to claim 20, wherein an axial wall means is connected to said barrier and is in part at least tubular and extends axially from said barrier in at least partial surrounding relationship to the near end portion of the piston, and said mechanical spring is annular in shape and has a central opening forloosely receiving said axial wall means, and a bearing is radially received between said axial wall means and an inner side wall portion of'- the cavity, for guiding said axial wall means.

22. A motor according to claim 21, wherein a fluid containing chamber exists axially between said transverse wall and said piston and the fluid therein provides a cushioning stop for said piston.

23. A gas spring powered impact tool, comprising:

a linear impact member;

a reciprocating linear hammer in line with said member;

a compressed gas spring'in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; and

a hammer return hydraulic system including means for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke. r

24. An impact tool according to claim 24, including means for trapping a body of the hydraulic fluid being a portion of the hammer and a portion of the housing to provide a fluid stop at the end of the power stroke.

25. A linear reciprocating motor comprising:

an elongated piston in said cavity;

hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve'member, resulting in the force of the hydraulic fluid beingre'moved from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, and means in said housing defining an expansible chamber for receiving some of the hydraulic fluid when the piston is at least partially retracted against the spring, said means including a movable surface on said valve member, said movable surface on said valve member being directed such that fluid in said chamber acting on said movable surface tends to urge the valve member towards its second position. 26. A motor according to claim 25, further comprising means in said housing including a portion of said piston for trapping fluid in said chamber, so that said fluid will hold the valve member in its second position,

until the piston has moved a predetermined distance an elongated piston in said cavity;

hydraulic means for driving the piston endwise through the cavity in the oppositedirection, in op position to the force of said spring means, withsaid spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, andmeans for delivering a hydraulicfluid to said transverse'wall and said pressure surface, including controlvvalve means comprising a linear re ciprocating valve member movable between a first position in which hydraulic fluid is admitted tothe pressuresurface and the transverse wall, formovingthe piston against the spring meansand compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface'isblocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, valvemember having a first end portion which is in communication with the'inflowing hydraulic fluid and receives an endwise force therefrom tending, to move said valve member towards its first position, and a second end portion subject to the force of said spring means, with the force of said spring means tending to move the valve member in the opposite direction towards its second position, with said inflowing hydraulic fluid by itself exerting: a larger force on said valve member and with said valve means further comprising means for directing some of the hydraulic fluid against the valve member, to exert a force on the valve member acting in the same direction as the force exerted by the spring means, when the valve member is in its first position and the piston is against the spring means and has compressed same, with the combined forces of said spring means and said hydraulic'fluid.

being larger than the force of said inflowing hydraulic fluid and being sufficient to move said valve member into its second position.

28. A linear reciprocating motor comprising:

an elongated piston in said cavity;

spring means exerting a force on said piston tending to drive it-endwise through saidcavity towards said transverse wall;

hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pres sure surface on said piston spaced axially from said, transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, ineluding control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a secondposition in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the springmeans endwise through the cavity towards said transverse wall, and means in said housing including a portion of said piston for transferring the hydraulic fluid from said pressure surface into an expansible chamber near the spring end of said piston which chamber is bounded in part by a movable surface on said piston, said chamber including outlet means leading to exhaust, so that when the piston is moved by new hydraulic fluid towards said spring the fluid in said chamber is forced therefrom by the piston through the outlet means to exhaust.

29. A gas spring powered impact tool, comprising:

a linear impact member;

a reciprocating linear hammer in line with said member; i

a compressed gas spring in line with said hammer, fo

forcibly driving said hammer endwise through a power stroke, into impacting contact with said member;

a hammer return hydraulic system including means for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gasspring can drivethe hammer through its power stroke; and

means for isolating the hammer from the force of said spring means before the hammer reaches the end of itspower stroke, so that the hammer is free to coast to a stop position before reversing its direction of travel.

30. A gas spring powered impact tool, comprising:

a linear impact member;

a reciprocating-linear hammer in line with said memher;

a compressed gas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; and

a hammer return hydraulic system including means responsive to the position of said hammer for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke, said means releasing hydraulic fluid from the hammer immediately following each retraction of said hammer, and said means delivering additional hydraulic fluid pressure against the hammer, for again retracting the hammer, in response to each travel of the hammer through a power stroke.

31. A gas spring powered impact tool according to claim 37, wherein said hydraulic system includes a valve member having a first end portion which is in communication with the inflowing hydraulic fluid and receives an endwise force therefrom tending to move said valve member towards a first position in which hydraulic fluid is admitted to said hammer, a second end portion, biasing force means acting on said second end portion and tending to move the valve member in the opposite direction towards a second position in which it blocks flow of hydraulic flow to the hammer and the hydraulic fluid pressure on the hammer is released, with said inflowing hydraulic fluid by itself exerting a larger force on said valve member than said biasing force means, and valve means for directing some of the hydraulic fluid against the valve member, to exert a force on the valve member acting in the same direction as the biasing force when the valve member is in its first position and the piston is against the compressed gas spring and has compressed same, with the combined forces of said biasing force and said hydraulic fluid being larger than the force of said inflowing hydraulic fluid and being sufficient to move said valve member into its second position.

32. An impact tool according to claim 30, wherein said means for alternately delivering hydraulic fluid to and exhausting it from the hammer includes valve member movable between a first position in which the hydraulic fluid is admitted to the hammer, for moving said hammer against said spring means and compressing the latter, and a second position in which said fluid is exhausted from the hammer and additional flow to the, hammer is blocked by said valve member, resulting the spring means endwise through its power stroke.

33. A gas spring powered impact tool, comprising:

a linear impact member;

a reciprocating linear hammer in line with said mema compressedrgas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; I

a hammer return hydraulic system including means responsive to the position of said hammer for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energyin the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke; and

means for trapping a body of the hydraulic fluid between a portion of the hammer and a portion of the housing to provide a fluid stop at the end of the power stroke.

Claims

1. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a linear reciprocating valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, said valve member having a first end portion which is in communication with the inflowing hydraulic fluid and receives an endwise force therefrom tending to move said valve member towards its first position, a second end portion, biasing force means acting on said second end portion and tending to move the valve member towards its second position, with said inflowing hydraulic fluid by itself exerting a force on said valve member that is larger than then biasing force, said valve means further comprising means for directing some of the hydraulic fluid against the valve member, to exert a force on the valve member acting in the same direction as the biasing force wHen the valve member is in its first position, with the combined forces of said biasing force means and said hydraulic fluid being larger than the force of said inflowing hydraulic fluid and being sufficient to move said valve member into its second position.

2. A motor according to claim 32, wherein the spring means is a body of a compressible fluid sealed within a chamber which is expansible towards the piston.

3. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, wherein said valve member is annular and surrounds a portion of said piston, said valve member includes a first end surface which is seated against a portion of said transverse surface when the valve member is in its second position, and a second end surface which is subjected to the force of the spring means, such force tending to urge the valve member towards said transverse surface, and said housing includes passageway means for delivering hydraulic fluid to the first end surface of said valve member, for exerting a force on said first end surface which moves the valve member from its second position into its first position.

4. A motor according to claim 3, wherein said housing includes an internal tubular guide for said valve member in which said valve member moves, means forming a bypass chamber which at least partially surrounds the valve member, said valve member including side wall opening means through which the hydraulic fluid flows from the piston pressure surface into said by-pass chamber when the valve member is in its second position and the piston is traveling through its power stroke.

6. A motor according to claim 5, wherein the tubular guide for said valve member includes means forming an expansible chamber with said valve member, in surrounding relationship to said valve member, and said valve member includes a piston ring portion defining a movable wall of said chamber, and said valve member includes side wall opening means through which the hydraulic fluid flows from the region of the piston pressure surface into said expansible chamber when the valve member is in its first position and the piston is retracted against the spring means, whereby the hydraulic fluid exerts a force on said piston ring which in combination with the spring means fOrce on the valve member acts to move the valve member from its first position into its second position.

10. A motor according to claim 9, wherein said housing includes means forming an internal annular seat generally at the entrance to said by-pass chamber, and said valve member includes an exterior annular closure portion which seats tightly against said seat when the valve member is in its first position, and prevents hydraulic fluid from flowing into the by-pass chamber so that it instead exerts a force on the pressure surface of the piston.

13. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall, and means for delivering a hydraulic fluid to said surface, including control valve means movable between a first position in which the hydraulic fluid is admitted to the pressure surface, for moving the piston against the spring means and compressing the latter, and a second position in which the hydraulic fluid is exhausted from the pressure surface, resulting in the piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall; and limit means for isolating the piston from the force of said spring means before the piston reaches the transverse wall, so that the piston is not driven hard against the transverse wall by the spring means but is free to coast to a stop position as it approaches the transverse wall before reversing its direction of travel.

14. A motor according to claim 13, wherein a fluid containing chamber exists axially between said transverse wall and said piston and the fluid therein provides a cushioning stop for said piston.

16. A motor according to claim 15, wherein the limit means comprises a barrier for the fluid spring chamber and means for arresting movement of said barrier independently of said piston, positioned so that the barrier is stopped before the piston reaches said transverse wall and serves to isolate the spring force from the piston.

20. A motor according to claim 15, wherein the stop member for said wall means is a mechanical spring.

21. A motor according to claim 20, wherein an axial wall means is connected to said barrier and is in part at least tubular and extends axially from said barrier in at least partial surrounding relationship to the near end portion of the piston, and said mechanical spring is annular in shape and has a central opening for loosely receiving said axial wall means, and a bearing is radially received between said axial wall means and an inner side wall portion of the cavity, for guiding said axial wall means.

23. A gas spring powered impact tool, comprising: a linear impact member; a reciprocating linear hammer in line with said member; a compressed gas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; and a hammer return hydraulic system including means for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke.

25. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, and means in said housing defining an expansible chamber for receiving some of the hydraulic fluid when the piston is at least partially retracted against the spring, said means including a movable surface on said valve member, said movable surface on said valve member being directed such that fluid in said chamber acting on said movable surface tends to urge the valve member towards its second position.

26. A motor according to claim 25, further comprising means in said housing including a portion of said piston for trapping fluid in said chamber, so that said fluid will hold the valve member in its second position, until the piston has moved a predetermined distance through its power stroke.

27. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through said cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a linear reciprocating valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, valve member having a first end portion which is in communication with the inflowing hydraulic fluid and receives an endwise force therefrom tending to move said valve member towards its first position, and a second end portion subject to the force of said spring means, with the force of said spring means tending to move the valve member in the opposite direction towards its second position, with said inflowing hydraulic fluid by itself exerting a larger force on said valve member and with said valve means further comprising means for directing some of the hydraulic fluid against the valve member, to exert a force on the valve member acting in the same direction as the force exerted by the spring means, when the valve member is in its first position and the piston is against the spring means and has compressed same, with the combined forces of said spring means and said hydraulic fluid being larger than the force of said inflowing hydraulic fluid and being sufficient to move said valve member into its second position.

28. A linear reciprocating motor comprising: a housing including an elongated piston cavity defined in part by a transverse wall; an elongated piston in said cavity; spring means exerting a force on said piston tending to drive it endwise through saId cavity towards said transverse wall; hydraulic means for driving the piston endwise through the cavity in the opposite direction, in opposition to the force of said spring means, with said spring means being compressed by said piston as it so moves, said hydraulic means including a pressure surface on said piston spaced axially from said transverse wall and in fluid communication therewith, and means for delivering a hydraulic fluid to said transverse wall and said pressure surface, including control valve means comprising a valve member movable between a first position in which hydraulic fluid is admitted to the pressure surface and the transverse wall, for moving the piston against the spring means and compressing the latter, and a second position in which such hydraulic fluid is removed from said pressure surface and flow of additional hydraulic fluid to said pressure surface is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said piston and said piston being forcibly moved by the spring means endwise through the cavity towards said transverse wall, and means in said housing including a portion of said piston for transferring the hydraulic fluid from said pressure surface into an expansible chamber near the spring end of said piston which chamber is bounded in part by a movable surface on said piston, said chamber including outlet means leading to exhaust, so that when the piston is moved by new hydraulic fluid towards said spring the fluid in said chamber is forced therefrom by the piston through the outlet means to exhaust.

29. A gas spring powered impact tool, comprising: a linear impact member; a reciprocating linear hammer in line with said member; a compressed gas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; a hammer return hydraulic system including means for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke; and means for isolating the hammer from the force of said spring means before the hammer reaches the end of its power stroke, so that the hammer is free to coast to a stop position before reversing its direction of travel.

30. A gas spring powered impact tool, comprising: a linear impact member; a reciprocating linear hammer in line with said member; a compressed gas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; and a hammer return hydraulic system including means responsive to the position of said hammer for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke, said means releasing hydraulic fluid from the hammer immediately following each retraction of said hammer, and said means delivering additional hydraulic fluid pressure against the hammer, for again retracting the hammer, in response to each travel of the hammer through a power stroke.

32. An impact tool according to claim 30, wherein said means for alternately delivering hydraulic fluid to and exhausting it from the hammer includes valve member movable between a first position in which the hydraulic fluid is admitted to the hammer, for moving said hammer against said spring means and compressing the latter, and a second position in which said fluid is exhausted from the hammer and additional flow to the hammer is blocked by said valve member, resulting in the force of the hydraulic fluid being removed from said hammer and said hammer being forcibly moved by the spring means endwise through its power stroke.

33. A gas spring powered impact tool, comprising: a linear impact member; a reciprocating linear hammer in line with said member; a compressed gas spring in line with said hammer, for forcibly driving said hammer endwise through a power stroke, into impacting contact with said member; a hammer return hydraulic system including means responsive to the position of said hammer for alternately delivering hydraulic fluid pressure against the hammer for moving it endwise against the compressed gas spring, for retracting the hammer and storing energy in the compressed gas spring, and releasing said hydraulic fluid from the hammer, so that the stored energy in the compressed gas spring can drive the hammer through its power stroke; and means for trapping a body of the hydraulic fluid between a portion of the hammer and a portion of the housing to provide a fluid stop at the end of the power stroke.